Sintering arrangement for enhancing removal of carbon from ceramic substrate laminates

ABSTRACT

There is disclosed a sintering arrangement for enhancing the removal of carbon from multilayer ceramic substrate laminate during the sintering thereof. A multilayer ceramic substrate laminate having metallic lines and vias is provided with a reducible metal oxide in close proximity to the substrate laminate. The multilayer ceramic substrate laminate contains a polymeric binder which upon heating depolymerizes into carbon. The substrate laminate is sintered in an atmosphere which is reducing with respect to the reducible metal oxide and which is oxidizing with respect to the carbon.

This is a division of application Ser. No. 07/523,949, filed May 16,1990, now U.S. Pat. No. 5,053,361, which is a division of applicationSer. No. 07/220,192 filed Jul. 18, 1988, now U.S. Pat. No. 4,971,738.

BACKGROUND OF THE INVENTION

The present invention relates to the removal of organic binders fromceramic substrate laminates. More specifically, the present inventionteaches a method and sintering arrangement for achieving superior binderremoval while sintering a ceramic body in an oxygen-containingenvironment without oxidizing any associated metallurgy.

In the field of microelectronics, ceramics serve as superior insulatorsand carriers for metallurgy. The ceramics can be sintered to a densestate wherein they exhibit strength as well as favorable dielectricproperties Ceramics may be pre-fired and subsequently metallized, as isdone commonly for simple chip carriers; however, in packages for use inhigh performance computers, greater circuit densities are desirable.Greater circuit density may be realized in a multilayer body whereinunfired ceramics are cast into sheets, patterned and metallized andsubsequently aligned and stacked. The stack is then laminated and firedto form a fully sintered body.

The firing of stacked and metallized ceramics involves careful selectionof materials and processing conditions. The firing temperatures andenvironment must be compatible with the metallurgy associated with theceramic. Furthermore, the binders and plasticizers which are added tothe ceramic slurry must be removed prior to the densification of theceramic particles. Typically, the binders and plasticizers are chosen sothat they depolymerize into volatile hydrocarbons and carbonaceousresidues upon heating to a particular temperature. If the carbonaceousresidue (hereinafter referred to simply as carbon) is not fully removed,the ceramic obtained will be porous, weak and of inferior insulatingcharacteristics.

The time-temperature-ambient regimen used in substrate laminatesintering is generally called the firing cycle. Various firing cycleshave been proposed wherein oxygen in the form of steam is provided tothe substrate laminate in carefully controlled amounts in order tofacilitate the removal of the carbon. The steam reacts with the carbonto form carbon dioxide and hydrogen As taught in Herron et al. U.S. Pat.No. 4,234,367, the partial pressure of oxygen in the ambient iscontrolled by introducing controlled amounts of free hydrogen with thesteam, thereby recapturing any free oxygen to prohibit it from reactingwith the associated metallurgy

Herron et al. further illustrate a system wherein the associatedmetallurgy is copper and the ceramic is a glass ceramic. To allow anyamount of the copper to be oxidized gives rise to expansion problemswhereby the copper oxide formed would expand in the internal layers andplace tremendous stresses on the ceramic.

Kamehara et al. U.S. Pat. No. 4,504,339 also teaches a system for firinga ceramic and metal stack in an oxygen-containing ambient. Kamehara etal. similarly claims control of the partial pressure of the oxygen atlow pre-densification temperatures to prohibit oxidation of theconductors.

Herron et al. U.S. Pat. No. 4,627,160 have proposed adding a catalyst tothe slurry of ceramic particles, binder and solvent as an aid inpromoting the effective removal of the carbonaceous materials. Proposedfor use as catalysts are copper and copper oxides. As a practicalmatter, the maximum amount of catalyst is limited to about 0.15 weightpercent. More than this will adversely affect the strength anddielectric properties of the ceramic substrate. It has been found thatthe catalyst is effective in use. There, however, remains a problem inmaintaining the correct ratio of hydrogen to steam during the binderburnoff phase of the firing cycle.

Brownlow et al. U.S. Pat. No. 4,474,731 proposes the use of nickel oxideas the catalyst to promote the removal of carbonaceous materials from aceramic substrate.

Marshall U.S. Pat. No. 4,189,760 proposes a capacitor wherein layers ofceramic are coated with nickel oxide Thereafter, the nickel oxide isreduced to nickel which may then serve as the capacitor electrodes.

Dirstine U.S. Pat. No. 4,386,985 proposes additions of nickel oxide to aceramic capacitor to increase the dielectric constant of the capacitor.It was also found that the nickel oxide prevents the nickel electrodesfrom dissolving in the ceramic during sintering.

Treptow U.S. Pat. No. 2,993,815 discloses the formation of a ceramicprinted circuit board wherein a layer of copper is formed on arefractory substrate. Initially, copper or copper oxide is mixed with aglass-containing paste and then applied to the surface of a greenrefractory substrate. Thereafter, the coated substrate is fired in anoxidizing atmosphere to remove the carbonaceous residues and also tomake sure that the copper that is present is in the form of copperoxide. During this step a refractory substrate-to-glass-to-copper bondis formed. Finally, the coated substrate is heated in a reducingatmosphere to reduce the copper oxide to copper.

Kato et al. discloses a ceramic composition containing a copper oxide.During a reducing heat treatment, the copper ions move to the surface ofthe ceramic. Thereafter, the ceramic coated with copper ions undergoesheating in an oxidizing atmosphere followed by heating in a reducingatmosphere. The end result is a ceramic substrate having a very thincoating of copper.

The disclosure of all of the above references is incorporated byreference herein.

Notwithstanding the above teachings of those skilled in the art, thereremains a real need to improve the burnoff of carbonaceous residues.

This need arises from the fact that the process to remove thecarbonaceous residues as taught in, for example, the Herron et al.references is extremely slow. It would be very desirable to be able toimprove the process so as to make the removal of carbonaceous residuesmore effective and efficient.

It is, accordingly, an object of the invention to improve the burnoff ofcarbonaceous residues.

It is another object of the invention to reduce the time for effectiveburnoff of carbonaceous residues.

It is yet another object of the invention to maintain tighter control ofthe ambient during burnoff of the carbonaceous residues

These and other objects of the invention will become more apparent afterreferring to the following description considered in conjunction withthe accompanying drawings.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention relates to a method of enhancing the removalof carbon from multilayer ceramic substrate laminates during thesintering thereof, comprising the steps of:

providing a multilayer ceramic substrate laminate having metallic linesand vias and a reducible metal oxide in close proximity to themultilayer ceramic substrate laminate, the multilayer ceramic substratelaminate containing a polymeric binder which upon heating depolymerizesinto carbon; and

sintering the substrate laminate in an atmosphere which is reducing withrespect to the reducible metal oxide and which is oxidizing with respectto the carbon.

Another aspect of the invention relates to a sintering arrangement forenhancing the removal of carbon from multilayer ceramic substratelaminate during the sintering thereof, comprising:

a ceramic substrate laminate having metallic lines and vias andcontaining a polymeric binder which upon heating depolymerizes intocarbon; and

a reducible metal oxide on at least one surface of the substratelaminate wherein the reducible metal oxide is chosen such that when thesubstrate laminate is sintered in an atmosphere which is oxidizing withrespect to the carbon, the reducible metal oxide undergoes reduction toform an adherent layer of metallurgy on the surface of the multilayerceramic substrate.

A further aspect of the invention relates to a sintering arrangement forenhancing the removal of carbon from multilayer ceramic substratelaminate during the sintering thereof, comprising:

a multilayer ceramic substrate laminate having metallic lines and viasand a polymeric binder which upon heating depolymerizes into carbon; and

at least one setter tile proximate with the multilayer ceramic substratelaminate, the setter tile comprising a refractory oxide and a reduciblemetal oxide wherein the reducible metal oxide is chosen such that uponsintering the ceramic substrate laminate in an atmosphere which isoxidizing with respect to the carbon, the reducible metal oxideundergoes reduction to the non-oxide form.

A final aspect of the invention relates to a partially sintered settertile composition comprising copper oxide and a refractory oxide with thecopper oxide constituting at least 20 weight % of the composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a known multi-layer ceramic substrate.

FIG. 2 is a side view of a multi-layer ceramic substrate laminate andsintering arrangement according to the invention.

FIG. 3 is a graph illustrating the equilibrium between copper, carbonand their oxides in a H₂ /H₂ O ambient.

FIG. 4 is an exploded perspective view of a setter tile according to theinvention.

FIG. 5 is a cross-sectional view of another embodiment of a setter tileaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures in more detail and particularly referring toFIG. 1, there is shown a sintered multi-layer ceramic substrate 10. Themulti-layer ceramic substrate is comprised of a plurality of layers ofceramic material one of which 12 is shown. Each of the layers of theceramic material has metallic lines 14 and vias 16. Additionally, themulti-layer ceramic substrate comprises top surface metallurgy 18 andbottom surface metallurgy (not shown).

Referring now to FIG. 2, the method according to the invention will bedescribed. According to the invention there is disclosed a method ofenhancing the removal of carbon from multi-layer ceramic substratelaminate during their sintering. The method comprises the steps of firstproviding an unfired multi-layer ceramic substrate laminate 10' havingmetallic lines 14 and vias 16. The method further comprises providing areducible metal oxide in close proximity to the multi-layer ceramicsubstrate laminate 10'. The multi-layer ceramic substrate laminatecontains a polymeric binder which upon heating depolymerizes into carbonas is well known in the art.

In the sintering of multi-layer ceramic substrate laminates thesintering arrangement will typically further comprise, as disclosed inU.S. patent application Ser. No. 859,093, the disclosure of which isincorporated by reference herein, a non-sintering ceramic sheet 22 ontop of the ceramic substrate laminate and a non-sintering ceramic sheet24 underneath the ceramic substrate laminate. Each of the non-sinteringceramic sheets may be, for example, an alumina green sheet. On top ofthis sintering arrangement will be a weight 26. The entire sinteringarrangement sits on a setter tile 28. In place of weight there may be asecond setter tile.

The next step in the method comprises sintering the substrate laminate10' in an atmosphere which is reducing with respect to the reduciblemetal oxide and which is oxidizing with respect to the carbon. Such asintering cycle is well known and is disclosed in the Herron et al.,patents discussed previously. The steps of sintering converts thesubstrate laminate 10' into the substrate 10.

The preferred ceramic substrate laminate according to the invention hasmetallic lines and vias made from copper or copper alloys. It should beunderstood however, that the copper or the copper alloys may be replacedby other metals or alloys of good conductivity such as, nickel,molybdenum, silver, palladium or mixtures thereof. Further, it ispreferred that where the metallic lines and vias are copper or copperalloys the reducible metal oxide is a copper oxide selected from thegroup consisting of Cu₂ O (cuprous oxide) and CuO (cupric oxide). If oneof the other metals or alloys is used as the metallic lines and viasthen the reducible metal oxide will be replaced so as to be the oxide ofthat other metal or alloy.

The most important aspect of the present invention is the provision ofthe reducible metal oxide in close proximity to the multilayer ceramicsubstrate laminate. As taught in Herron et al. U.S. Pat. No. 4,234,367,binder burnoff occurs during the steam segment of the firing cycle.Generally, the temperature for binder burnoff will be between about 700°and 785° C. The desired atmosphere is such that the ratio of H₂/steam=10⁻⁴, (at 785° C.) which is an optimal atmosphere for notoxidizing copper (assuming copper lines and vias) while oxidizing carbonfrom the organic binders. This is marked as point X in FIG. 3. It shouldbe noted that FIG. 3 is taken directly from the Herron et al. U.S. Pat.No. 4,234,367. Similar reasoning will apply to other metallurgiesbesides copper. For purposes of illustration, and not limitation, coppermetallurgy is discussed. It should be understood, however, that othermetals and alloys are included within the scope of the invention.

In practice, this ideal condition is not realized During the reaction

    C+2H.sub.2 O(steam)=CO.sub.2 +2H.sub.2

hydrogen is continuously liberated in situ which makes the actualcondition for the ratio H₂ /H₂ O>>10⁻⁴. In the initial stages the H₂ /H₂O ratio in the vicinity of the substrates starts close to point Ybecause the supply of the H₂ O ambient is diffusion limited and theequilibrium H₂ /H₂ O condition for the C and H₂ O reaction is maintainedby the reaction. When most of the carbon is removed by the reaction,liberation of H₂ is decreased and diffusion no longer limits the H₂ /H₂O ratio; therefore, conditions begin to move towards point X.

Because the reaction rate decreases with increasing local H₂concentration, the binder removal rate is not at the maximum asrecommended by Herron et al., U. S. Pat. No. 4,234,367 and hence inpractice, results in excessively long times required for binder removal.The present invention provides a method of practicing the steam segmentat nearly ideal maximum rates for the carbon-steam reaction. The idealmaximum rate for a copper containing system occurs when the ratio of H₂/H₂ O is always at point Z as shown in FIG. 3. This is the equilibriummaintained by the following reaction,

    2Cu+H.sub.2 O=Cu.sub.2 O+H.sub.2

This condition is always maintained in the vicinity of the substratelaminate by having both Cu and Cu₂ O proximate to the multilayer ceramicsubstrate laminate. If hydrogen or steam is in excess of the equilibriumratio point Z, the reaction shifts to form either Cu or Cu₂ O to balancethe shift. This means that the conditions become self-regulating as longas both Cu and Cu₂ O are present in some amount proximate to thesubstrate.

In the present invention, the above regulating condition is achieved byinitially starting with CuO or Cu₂ O proximate to the substrate laminateAs hydrogen is liberated from the carbon-steam reaction, the followingreactions take place,

    2CuO+H.sub.2 =Cu.sub.2 O+H.sub.2 O (initially)

    Cu.sub.2 O+H.sub.2 =2Cu+H.sub.2 O (final equilibrium)

These reactions provide consumption of the excess hydrogen and thegeneration of more steam locally.

By knowing the amount of binder in the substrate laminate to be reacted,the amount of CuO or Cu₂ O to be initially placed proximate to thesubstrate laminate is determined such that there is an excess of Cu₂ Oleft, over and above the amount required to consume all of the hydrogenfrom the carbon reaction.

Both Cu₂ O or CuO can be present, but the amount required is greater forCu₂ O than for CuO because of its lower oxygen content.

This kind of self-regulating buffered system maintains the ideal H₂ /H₂O ratio directly at the surface of the substrate laminate. The presentinvention should thus be considered as an improvement of, rather than asubstitute for, the process of Herron et al. U.S. Pat. No. 4,627,160wherein a copper oxide or other reducible metal oxide is incorporated inthe ceramic substrate laminate itself. While the copper oxide catalystwithin the ceramic substrate laminate aids in the removal of carbon fromthe ceramic substrate laminate, the additional reducible metal oxide ofthe present invention in proximity to the multilayer ceramic substratelaminate serves to enhance that removal of carbon, as will be shown inmore detail hereafter.

Typically, the polymeric binder will comprise polyvinyl butyral (PVB)resin. However, it is within the scope of the invention for thepolymeric binder to comprise polymethyl methacrylate (PMMA),polyalphamethyl styrene, or other well known ceramic binder systems.

It is most preferred that the ceramic substrate laminate comprises aceramic selected from the group consisting of cordierite type glassceramics and spodumene type glass ceramics such as that disclosed inKumar et al. U.S. Pat. Nos. 4,413,061 and 4,301,324, the disclosures ofwhich are incorporated by reference herein.

The preferred sintering atmosphere is an atmosphere of steam andhydrogen wherein the hydrogen/steam ratio is in the range of 10⁻⁴ to10⁻⁶.5. The sintering temperature must be less than the melting point ofthe metallic lines and vias.

While the reducible metal oxide must be in close proximity to themulti-layer ceramic substrate laminate 10' it may be situated in anumber of different locations just so long as it is proximate to thesubstrate laminate. Thus, the reducible metal, oxide may be on at leastone surface of the ceramic substrate laminate. For example, as shown inFIG. 2, the reducible metal oxide 20 is directly on the top (orhorizontal) surface of the ceramic substrate laminate 10'. Additionally,the reducible metal oxide 20 may also be located directly on the bottomsurface of the ceramic substrate laminate as well. When the reduciblemetal oxide is directly on a surface of the multilayer ceramic substratelaminate the reducible oxide, upon reducing to the metal, forms anadherent layer of metal on the ceramic substrate laminate and then thesubstrate. In practice, what happens is that the reducible metal oxidefirst at least partially dissolves into the ceramic substrate laminateand subsequently forms an adherent layer of metal on its surface. Anadvantage of forming this layer of metal directly on the ceramicsubstrate is that instead of the top or bottom surface metallurgy beingscreened on and then fired, the metallurgy may be simply formed directlyon the substrate in situ and then patterned by photolithographic steps.

Alternatively, the reducible metal oxide may be located in at least onesetter tile proximate to the ceramic substrate laminate. This latterembodiment will be discussed in more detail shortly The sinteringarrangement as shown in FIG. 2 thus represents one aspect of theinvention.

There may further be a sintering arrangement according to the inventionfor enhancing the removal of carbon from multi-layer ceramic substratelaminates during their sintering wherein at least one setter tile, suchas setter tile 28 in FIG. 2, is proximate with the multi-layer ceramicsubstrate laminate. The setter tile 28 comprises a refractory oxide anda reducible metal oxide. The reducible metal oxide is chosen such thatupon sintering the ceramic substrate laminate in an atmosphere which isoxidizing with respect to the carbon, the reducible metal oxideundergoes reduction to the non-oxide (or metallic) form. In oneembodiment the setter tile may be in direct contact with the ceramicsubstrate laminate.

The refractory oxide in the setter tile may be any refractory oxidealthough it is preferred that it be alumina (A1₂ O₃), silica (SiO₂),magnesia (MgO), zirconia (ZrO₂) or combinations thereof.

It is most preferred that the setter tile is partially sintered, therebyensuring a porous body. The porosity is desirable since it allows theambient gases to flow through the setter tile and contact the ceramicsubstrate laminate, thereby rendering more efficient the removal of thebinder decomposition products. It should be understood that partiallysintered means having at least 40% porosity and optimally, 45-50%porosity. For a 92 weight % A1₂ O₃, 8 weight % glass setter tile, forexample, a partially sintered body may be obtained by sintering between1000-1350° C. for about 12 to 24 hours after a preliminary heating cycleat lower temperatures for removal of the binder.

Referring now to FIG. 4 there is shown an exploded perspective view of asetter tile 128 according to the invention. Setter tile 128 comprises aplurality of layers 130 of refractory oxide having the reducible metaloxide screened thereon. Thus each layer 130 has a pattern 132 ofreducible metal oxide screened thereon. On either side of the pluralityof screened layers 130 is at least one layer 134 which simply comprisesrefractory oxide without any reducible metal oxide thereon. Since eitherside of the setter tile 128 has a plain ceramic surface, the setter tile128 may be placed in direct contact with the ceramic substrate withoutthe necessity of the plain non-sintering ceramic sheets 24 and 22 asdiscussed previously.

Referring now to FIG. 5 there is shown another embodiment of a settertile according to the invention. In this case setter tile 228 comprisesrefractory oxide 230 having the reducible metal oxide 232 dispersedtherein. This particular setter tile 228 has porosity 234 which aids inthe flow of gases from the ambient to the surface of the multi-layerceramic substrate laminate.

As noted previously, the amount of reducible metal oxide present shouldbe in excess of that required for complete buffering of the ambient.This in turn will vary depending on the amount of binder present. Ingeneral, the amount of reducible metal oxide present in the fired settertile should be between about 20 and 70 weight percent, with theremainder being the refractory oxide.

In either of the embodiments of FIGS. 4 or 5 the reducible metal oxideis preferably a copper oxide selected from the group consisting ofcuprous oxide (Cu₂ O) and cupric oxide (CuO). Of course, as describedpreviously the reducible metal oxide may be changed if the metal linesand vias of the multi-layer ceramic substrate laminate are other thancopper or copper alloys.

During the sintering cycle most of the initial copper oxide in thebuffered setter tile has been converted to copper metal by the hydrogenfrom the carbon reaction. To regenerate these tiles they are heated inair to between 500° and 800° C. to convert all of the metal into CuO(only CuO is stable in air at these temperatures, not Cu₂ O). The settertile is now ready to be reused in the next sintering cycle.

A final aspect of the invention relates to a partially sintered settertile composition comprising copper oxide and refractory oxide with thecopper oxide constituting at least 20 weight % of the composition. Thecopper oxide may be selected from the group consisting of cupric oxideand cuprous oxide. The refractory oxide may be any of those discussedpreviously.

The advantages and objects of the invention will become more apparentafter referring to the following examples.

EXAMPLE 1

Glass powder of approximate composition by weight of 20% magnesiumoxide, 25% aluminum oxide with the remainder being silicon dioxide andvery small amounts of nucleating agents such as phosphorus pentoxide andboron trioxide, was mixed, in a ball mill, with a suitable organicbinder such as polyvinyl butyral and solvents such asmethyl-isobutyl-ketone in appropriate proportions to yield a castableslurry. No copper oxide catalyst was added to the composition. Theslurry was then cast into green sheets of approximately 400-599 micronsin thickness by a doctor blading technique. After drying the greensheets to expel the solvents, they were cut to suitable dimensions andlaminated in a press under heat and pressure to form a monolithiclaminate A paste prepared by mixing cuprous oxide (Cu₂ O) and a suitablepaste vehicle such as Texanol (consisting of 70% by weight of cuprousoxide) was then screened over the top and bottom surfaces of thesubstrate laminate to form a layer of approximate thickness of 50microns. The prepared laminate was placed on a refractory setter tile. Asimilar setter tile was also placed on top of the laminate to exertdownward pressure on the laminate during sintering and constrain itssintering in the plane of the laminate. The assembly was then sinteredin a programmable furnace as follows. The initial heating of thelaminate was carried out in an inert ambient of nitrogen to decomposeand carbonize the binder. On reaching a temperature of about 700° C.,the sintering atmosphere was changed to one consisting of water vaporand hydrogen in the proportion of 10⁴ :1 at which carbon oxidizes whilecopper does not. After holding for several hours at this temperature,the laminate was heated in nitrogen for several hours to expel waterdissolved in the glass powder, before being heated to the finalsintering temperature of about 950° C. in a reducing ambient ofhydrogen. The laminate was cooled to room temperature in nitrogenambient.

The sintered, glass ceramic substrate thus prepared was found to have anintegral surface layer of pure copper metal of thickness of about 20microns. It was also found that the presence of the copper oxide layeron the substrate surface had aided in the complete removal of carbonresidues uniformly through its thickness.

By combining suitable photolithographic and etching techniques, circularpads were formed out of the integral copper layer on the sinteredsubstrate. The adhesion of the copper layer to the glass ceramic surfacewas then tested by soldering studs to the circular copper pads and pulltesting. The adhesion of the copper layer was found to be adequate andcomparable to conventionally formed thick or thin film metal patterns onthe glass ceramic surface.

EXAMPLE 2

Setter tiles were prepared in the following manner. A slurry of alumina,glass, binders, solvents and other organic additives was cast into greensheets. (The final composition after firing was 92 weight % alumina, 8weight % glass). Thereafter, a paste consisting of CuO and a suitablepaste vehicle such as PVB or ethyl cellulose was prepared. The CuOcomprised 82 weight % of the paste. The paste was then patterned in asquare hatch pattern, such as that shown in FIG. 4, on the green sheets.There was about 5 to 8 grams of paste per green sheet.

A plurality of the screened green sheets were stacked together. On thetop and bottom of the stack were 2 or 3 unscreened green sheets. Thestack was then laminated at 75° C. and 6000 psi pressure followed bypre-sintering at about 980° C. to remove the organics. The finallaminate had 45 to 50% open porosity.

A conventional glass-ceramic substrate laminate such as that describedin the Kumar et al. patents was prepared, except that the substratecontained about 0.15% copper oxide as taught in the Herron et al. U.S.Pat. No. 4,627,160. One setter tile was placed on the top and underneaththe bottom of the glass ceramic substrate laminate. The arrangement soformed then underwent a conventional sintering cycle. The temperature ofthe steam segment was 730° C. and the H₂ /H₂ O ratio was 10⁻⁴.

After 18 hours there was complete binder burnoff. Under the samesintering conditions, but without the copper oxide-containing settertile, binder burnoff would have occurred in about 30 hours.

EXAMPLE 3

Setter tiles were prepared by making a slurry of a compositionconsisting in weight percent of

    ______________________________________                                        CuO                49.99                                                      Al.sub.2 O.sub.3   25.26                                                      Butvar B-90        2.58                                                       Benzoflex          0.90                                                       Methanol           5.37                                                       Methylisobutylketone                                                                             16.12                                                      ______________________________________                                    

which was then cast into green sheets. Twenty green sheets werelaminated together under heat and pressure to form the tile which wasthen heated to about 965° C. to remove the binders and to partiallysinter it. The partially-sintered setter tiles contained about 40%connected porosity. The final composition of the setter tile was 66.33weight % CuO, 33.67 weight % A1₂ O₃.

Several conventional glass ceramic substrate laminates such as thatdescribed in the Kumar et al. patents were prepared, except that thesubstrates contained about 0.15 weight % copper oxide as taught in theHerron et al. U.S Pat. No. 4,627,160. In one set of experiments, onecopper-oxide containing setter tile was placed on the top and underneaththe bottom of some of the glass ceramic substrate laminates. The settertiles and substrate laminates were then sintered in a conventionalsintering cycle. The temperature of the steam segment was either 730° C.or 750° C. and the H₂ /H₂ O ratio was 10⁻⁴.

In a second set of experiments, glass ceramic substrate laminates weresintered with setter tiles which did not contain copper oxide. All otherexperimental variables were held constant.

The time required for binder burnoff (<300 ppm carbon in the glassceramic) was measured for each of the sintered glass ceramic substrates.The results are summarized in Table 1.

                  TABLE 1                                                         ______________________________________                                        Time Required for Binder Burnoff                                              Temperature of Setter Tile                                                                             Setter Tile                                          Steam Segment  with CuO  without CuO                                          ______________________________________                                        730° C. 12        22                                                   750° C.  9        14                                                   ______________________________________                                    

An examination of Table 1 thus convincingly shows the reduction in timefor binder burnoff was 45% (at 730° C.) and 36% (at 750° C.) when acopper oxide was incorporated in the setter tile.

It will be apparent to those skilled in the art having regard to thisdisclosure that other modifications of this invention beyond thoseembodiments specifically described here may be made without departingfrom the spirit of the invention. Accordingly, such modifications areconsidered within the scope of the invention as limited solely by theappended claims.

What is claimed is:
 1. A sintering arrangement for enhancing the removal of carbon from multilayer ceramic substrate laminates during the sintering thereof comprising:an unfired ceramic substrate laminate having nonoxide metallic lines and vias and containing a polymeric binder which upon heating depolymerizes into carbon; and a reducible metal oxide prior to sintering on at least one surface of the substrate laminate wherein the reducible metal oxide is chosen such that when the substrate laminate is sintered in an atmosphere which is oxidizing with respect to the carbon, the reducible metal oxide undergoes reduction to form an adherent layer of metallurgy on the surface of the multilayer ceramic substrate.
 2. The sintering arrangement of claim 1 wherein the metallic liens and vias are copper or copper alloys.
 3. The sintering arrangement of claim 1 wherein the reducible metal oxide is a copper oxide selected from the group consisting of CuO and Cu₂ O.
 4. The sintering arrangement of claim 1 wherein the polymeric binder comprises polyvinyl butyral resin.
 5. The sintering arrangement of claim 1 wherein the ceramic substrate laminate comprises a ceramic selected from the group consisting of cordierite glass ceramics and spodumene glass ceramics.
 6. A sintering arrangement for enhancing the removal of carbon from multilayer ceramic substrate laminates during the sintering thereof, comprising:an unfired multilayer ceramic substrate laminate having nonoxide metallic lines and vias and a polymeric binder which upon heating depolymerizes into carbon; and at least one setter tile proximate with the multilayer ceramic substrate laminate, the setter tile comprising refractory oxide and a reducible metal oxide prior to sintering wherein the reducible metal oxide is chosen such that upon sintering the ceramic substrate laminate in an atmosphere which is oxidizing with respect to the carbon, the reducible metal oxide undergoes reduction to the non-oxide form.
 7. The sintering arrangement of claim 6 wherein the setter tile is in direct contact with the ceramic substrate laminate.
 8. The sintering arrangement of claim 6 wherein the setter tile comprises a plurality of layers of refractory oxide having the reducible metal oxide screened thereon.
 9. The sintering arrangement of claim 6 wherein the setter tile comprises refractory oxide having the reducible metal oxide dispersed therein.
 10. The sintering arrangement of claim 6 wherein the setter tile is partially sintered.
 11. The sintering arrangement of claim 6 wherein the refractory oxide is selected from the group consisting of alumina, silica, magnesia, zirconia and mixtures thereof.
 12. The sintering arrangement of claim 1 wherein the metallic liens and vias are copper or copper alloys.
 13. The sintering arrangement of claim 6 wherein the reducible metal oxide is a copper oxide selected from the group consisting of CuO and Cu₂ O.
 14. The sintering arrangement of claim 6 wherein the polymeric binder comprising polyvinyl butyral resin.
 15. The sintering arrangement of claim 6 wherein the ceramic substrate laminate comprises a ceramic selected from the group consisting of cordierite glass ceramics and spodumene glass ceramics. 